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The variation of the mass-to-light ratios M/L of early type galaxies as function of their luminosities L is investigated. It is shown that the tilt β = 0.27 (in the B–band) of the fundamental plane relation M/L ∝ L β can be understood as a combination of two effects: about one-quarter (i.e. ∆β = 0.07) is a result of systematic variations of the stellar population properties with increasing luminosity. The remaining three-quarters (i.e. ∆β = 0.2) can be completely attributed to nonhomology effects that lead to a systematic change of the surface brightness profiles with increasing luminosity. Consequently, the observed tilt in the K–band (β = 0.17) where stellar population effects are negligible, is explained by nonhomology effects alone. After correcting for nonhomology, the mean value of the mass-to-light ratio of elliptical galaxies (M/LB) is 7.1±2.8 (1σ scatter).
Trujillo et al. (Fri,) studied this question.